If the working capital is inflating , then each year you need a bit more working capital.
So (for example) if the working capital required at time 0 is 100, and if it is inflating at 3% per year. Then at time 1 you need an extra 3 (3% x 100), which means that the total has grown to 103. So at time 2 you need an extra 3.09 (3% x 103), and so on.
At the end of the project you assume that all of the working capital is received back.